I was fortunate enough to pick up a pair of 104aBs locally for a tenner. Not quite the bargain it might have been given that when I initially hooked them up they sounded dreadful. Very muddy and muffled. BTW, the cabinets are rough too but it's the sound that I'm interested in, not so much the aesthetics.

It was immediately apparent that one of the tweeters (T27) wasn't working. A look on eBay and I was quickly up to speed on how much they fetch. Slightly deterred, I started off with a new set of capacitors for the crossovers. These have drastically improved the sound I'm pleased to say. However, on pulling out the woofers I discovered that one of them has been replaced by an SP1022 at some time in the past. It has the same dimensions as the proper one - SP1039 - but has a smaller diameter coil.

As it stands, I'm waiting for a single T27 and SP1039 to come up for sale. I could replace the T27s with modern equivalents for the same cost but I'd rather stay with the originals. Can anyone help with sourcing these? Quite happy to pay market price.

You'll see I'm a newbie and apologise if asking for help in a first post is bad form.

My first speakers were a pair of Coda IIIs mail-ordered fro Sevenoaks Hi-Fi in the early 80s together with a Marantz PM310 amp and Dual CS505 T/T, all long since passed on to friends.

It's a good question - sometimes the obvious can be easily overlooked. The fuses had blown but they'd been bridged using sweet paper in one and kitchen foil in the other. The duff tweeter is open circuit.

Has anyone tried opening up a T27? I've got nothing to lose and I'd like to see the damage. The metal diisc on the front through which the wires pass looks to be spot-welded in two points to the faceplate.

Ah right I see. The fuses saved my tweeters on few occasions, I use my 104aB's in my small project studio and mistakes can happen when I monitor. Last time I accidentally pushed up the wrong fader resulting in very loud feedback and instead of frying my tweeter it blew the fuse.. phew

Has anyone tried opening up a T27? I've got nothing to lose and I'd like to see the damage. The metal diisc on the front through which the wires pass looks to be spot-welded in two points to the faceplate.

The diaphragm along with the faceplate disc around it are glued to the metal plate using two sided adhesive tape or something like it.

A couple of decades ago, when there were still spares for these, I obtained two diaphragms (that come as a unit with the voice coil) to fix my T27s that were the victims of a wild school ending party. Pretty easy to fix as the "rods" that you describe as spot welds are acting as guides to affix the new diaphragm where it should.

I got around to opening up the duff tweeter to have a look at the damage. The coil had become detached from the diaphragm and had dropped into the body of the driver with only one wire attached. It was really tricky getting the coil out and I unwound six inches of copper wire from it in the process.

Testing the resistance it showed 5.1 ohms so I decided to have a go at putting it back together. I used Ronseal floor varnish to stick it back onto the diaphragm positioniing it as near to the end of the 'tube' as possible ie closest to the magnet. I cheated a little with the tails not taking them to the outside which would compromise the dome's attachment, bridging the gap straight to the terminals instead with a little insulating tape on them to avoid shorting with the body. There was enough sticky left on the plate to just squeeze it back together satisfactorily.

The result - sounds perfect! I would have given it 10% chance when I opened it up.